Method and apparatus for electromagnetic treatment of the skin, including hair depilation

ABSTRACT

Apparatus and methods for electromagnetic skin treatment, including the removal of hair. Devices include pulsed light sources such as flashlamps for providing electromagnetic treatment of the skin, including hair removal. The devices and methods provide for the removal of large numbers of hairs at the same time, rather than on a hair by hair basis.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.08/912,764, filed Aug. 18, 1997 now U.S. Pat. No. 6,280,438, which is acontinuation-in-part of U.S. application Ser. No. 08/508,129, filed Jul.27, 1995, now U.S. Pat. No. 5,720,772, issued on Feb. 24, 1998; which isa continuation in part of U.S. application Ser. No. 08/477,479, filedJun. 7, 1995, now U.S. Pat. No. 5,620,478, issued on Apr. 15, 1997;which is a continuation of U.S. application Ser. No. 08/473,532, filedJun. 7, 1995, now U.S. Pat. No. 5,755,751, issued on May 26, 1998; whichis a continuation of U.S. application Ser. No. 08/383,509, filed Feb. 3,1995, now U.S. Pat. No. 5,626,631, issued on May 6, 1997; which is acontinuation-in-part of U.S. application Ser. No. 07/964,210, filed Oct.20, 1992, now U.S. Pat. No. 5,405,368, issued on Apr. 11, 1995; whichare incorporated herein by reference. U.S. application Ser. No.08/912,764 is also a continuation-in-part of U.S. application Ser. No.08/412,519, filed Mar. 29, 1995, now U.S. Pat. No. 5,683,380, issued onNov. 4, 1997, which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to the art of electromagneticskin treatment, including devices and methods for removing hair. Theinvention relates to a method and apparatus for utilizing a spatiallydispersed or extended pulsed light source such as a flashlamp andproviding treatment parameters for its use, and also relates to use ofdevices and methods that utilize electromagnetic energy to kill hairfollicles.

BACKGROUND OF THE INVENTION

It is known in the prior art to use electromagnetic radiation in medicalapplications for therapeutic uses such as treatment of skin disorders.For example, U.S. Pat. No. 4,298,005 to Mutzhas describes a continuousultraviolet lamp with cosmetic, photobiological, and photochemicalapplications. A treatment based on using the UV portion of the spectrumand its photochemical interaction with the skin is described. The powerdelivered to the skin using Mutzhas' lamp is described as 150 W/m²;which does not have a significant effect on skin temperature.

In addition to prior art treatment involving UV light, lasers have beenused for dermatological procedures, including Argon lasers, CO₂ lasers,Nd(Yag) lasers, Copper vapor lasers, ruby lasers and dye lasers Forexample, U.S. Pat. No. 4,829,262 to Furumoto, describes a method ofconstructing a dye laser used in dermatology applications. Two skinconditions which may be treated by laser radiation are external skinirregularities such as local differences in the pigmentation orstructure of the skin, and vascular disorders lying deeper under theskin which cause a variety of skin abnormalities including port winestains, telangiectasias, leg veins and cherry and spider angiomas. Lasertreatment of these skin disorders generally includes localized heatingof the treatment area by absorption of laser radiation. Heating the skinchanges or corrects the skin disorder and causes the full or partialdisappearance of the skin abnormality.

Certain external disorders such as pigmented lesions can also be treatedby heating the skin very fast to a high enough temperature to evaporateparts of the skin. Deeper-lying vascular disorders are more typicallytreated by heating the blood to a high enough temperature to cause it tocoagulate. The disorder will then eventually disappear. To control thetreatment depth a pulsed radiation source is often used. The depth theheat penetrates in the blood vessel is controlled by controlling thepulse width of the radiation source. The adsorption and scatteringcoefficients of the skin also affect the heat penetration. Thesecoefficients are a function of the constituents of skin and thewavelength of the radiation. Specifically, the absorption coefficient oflight in the epidermis and dermis tends to be a slowly varying,monotonically decreasing function of wavelength. Thus, the wavelength ofthe light should be chosen so that the absorption coefficient isoptimized for the particular skin condition and vessel size beingtreated.

The effectiveness of lasers for applications such as tattoo removal andremoval of birth and age marks is diminished because lasers aremonochromatic. A laser of a given wavelength may be effectively used totreat a first type of skin pigmentation disorder, but if the specificwavelength of the laser is not absorbed efficiently by skin having asecond type of disorder, it will be ineffective for the second type ofskin disorder. Also, lasers are usually complicated, expensive tomanufacture, large for the amount of power delivered, unreliable anddifficult to maintain.

The wavelength of the light also affects vascular disorder treatmentbecause blood content in the vicinity of the vascular disorders varies,and blood content affects the absorption coefficient of the treatmentarea. Oxyhemoglobin is the main chromophore which controls the opticalproperties of blood and has strong absorption bands in the visibleregion. More particularly, the strongest absorption peak ofoxyhemoglobin occurs at 418 nm and has a band-width of 60 nm. Twoadditional absorption peaks with lower absorption coefficients occur at542 and 577 nm. The total band-width of these two peaks is on the orderof 100 nm. Additionally, light in the wavelength range of 500 to 600 nmis desirable for the treatment of blood vessel disorders of the skinsince it is absorbed by the blood and penetrates through the skin.Longer wavelengths up to 1000 nm are also effective since they canpenetrate deeper into the skin, heat the surrounding tissue and, if thepulse-width is long enough, contribute to heating the blood vessel bythermal conductivity. Also, longer wavelengths are effective fortreatment of larger diameter vessels because the lower absorptioncoefficient is compensated for by the longer path of light in thevessel.

Accordingly, a wide band electromagnetic radiation source that coversthe near UV and the visible portion of the spectrum would be desirablefor treatment of external skin and vascular disorders. The overall rangeof wavelengths of the light source should be sufficient to optimizetreatment for any of a number of applications. Such a therapeuticelectromagnetic radiation device should also be capable of providing anoptimal wavelength range within the overall range for the specificdisorder being treated. The intensity of the light should be sufficientto cause the required thermal effect by raising the temperature of thetreatment area to the required temperature. Also, the pulse-width shouldbe variable over a wide enough range so as to achieve the optimalpenetration depth for each application. Therefore, it is desirable toprovide a light source having a wide range of wavelengths, which can beselected according to the required skin treatment, with a controlledpulse-width and a high enough energy density for application to theaffected area.

Pulsed non-laser type light sources such as linear flashlamps providethese benefits. The intensity of the emitted light can be made highenough to achieve the required thermal effects. The pulse-width can bevaried over a wide range so that control of thermal depth penetrationcan be accomplished. The typical spectrum covers the visible andultraviolet range and the optical bands most effective for specificapplications can be selected, or enhanced using fluorescent materials.Moreover, non-laser type light sources such as flashlamps are muchsimpler and easier to manufacture than lasers, are significantly lessexpensive for the same output power and have the potential of being moreefficient and more reliable. They have a wide spectral range that can beoptimized for a variety of specific skin treatment applications. Thesesources also have a pulse length that can be varied over a wide rangewhich is critical for the different types of skin treatments.

In addition to being used for treating skin disorders, lasers have beenused for invasive medical procedures such as lithotripsy and removal ofblood vessel blockage. In such invasive procedures laser light iscoupled to optical fibers and delivered through the fiber to thetreatment area. In lithotripsy the fiber delivers light from a pulsedlaser to a kidney or gallstone and the light interaction with the stonecreates a shock wave which pulverizes the stone. To remove blood vesselblockage the light is coupled to the blockage by the fiber anddisintegrates the blockage. In either case the shortcomings of lasersdiscussed above with respect to laser skin treatment are present.Accordingly, a treatment device for lithotripsy and blockage removalutilizing a flashlamp would be desirable.

To effectively treat an area the light from the source must be focussedon the treatment area. Coupling pulsed laser light into optical fibersin medicine is quite common. The prior art describes coupling isotropicincoherent point sources such as CW lamps into small optical fibers. Forexample, U.S. Pat. No. 4,757,431, issued Jul. 12, 1988, to Cross, et al.discloses a method for focusing incoherent point sources with smallfilaments or an arc lamp with an electrode separation of 2 mm into asmall area. Point (or small) sources are relatively easy to focuswithout large losses in energy because of the small size of the source.Also, U.S. Pat. No. 4,022,534, issued May 10, 1977, to Kishner discloseslight produced by a flash tube and the collection of only a smallportion of the light emitted by the tube into an optical fiber.

However, the large dimension of an extended source such as a flashlampmakes it difficult to focus large fractions of its energy into smallarea. Coupling into optical fibers is even more difficult since not onlymust a high energy density be achieved, but the angular distribution ofthe light has to be such that trapping in the optical fiber can beaccomplished. Thus, it is desirable to have a system for coupling theoutput of a high intensity, extended, pulsed light source into anoptical fiber.

Hair can be removed permanently for cosmetic reasons by various methods,for example, by heating the hair and the hair follicle to a high enoughtemperature that results in their coagulation. It is known that blood iscoagulated when heated to temperatures of the order of 70° C. Similarly,heating of the epidermis, the hair and the hair follicle to temperaturesof the same order of magnitude will also cause their coagulation andwill result in permanent removal of the hair.

One common method of hair removal, often called electrolysis, is basedon the use of “electric needles” that are applied to each individualhair. An electrical current is applied to each hair through the needle.The current heats the hair, causes its carbonization and also causescoagulation of the tissue next to the hair and some coagulation of themicro vessels that feed the hair follicle.

While the electrical needle method can remove hair permanently or longterm, its use is practically limited because the treatment is painfuland the procedure is generally tedious and lengthy.

Light can also be used effectively to remove hair. For example, otherprior art methods of hair removal involve the application of pulsedlight, generally from coherent sources such as lasers. R. A. Harte, etal., in U.S. Pat. No. 3,693,623, and C. Block, in U.S. Pat. No.3,834,391, teach to remove hair by coagulating single hair with a lightcoupled to the individual hair by an optical fiber at the immediatevicinity of the hair. Similarly, R. G. Meyer, in U.S. Pat. No.3,538,919, removes hair on a hair by hair basis using energy from apulsed laser. Similar inventions using small fibers are described inU.S. Pat. No. 4,388,924 to H. Weissman, et al. and U.S. Pat. No.4,617,926 to A. Sutton. Each of these teach to remove hair one hair at atime, and are thus slow and tedious.

U.S. Pat. No. 5,226,907, to N. Tankovich, describes a hair removalmethod based on the use of a material that coats the hair and hairfollicle. The coating material enhances absorption of energy by thefollicles, either by matching the frequency of a light source to theabsorption frequency of the material, or by photochemical reaction. Ineither case the light source is a laser. One deficiency of such a methodand apparatus is that lasers can be expensive and subject to stringentregulations. Additionally, the coating material must be applied only tothe hair follicles, to insure proper hair removal and to prevent damageof other tissue.

Light (electromagnetic) energy used to remove hair must have a fluencesuch that sufficient energy will be absorbed by the hair and the hairfollicle to raise the temperature to the desired value. However, if thelight is applied to the surface of the skin other than at the preciselocation of a hair follicle, the light will also heat the skin tocoagulation temperature and induce a burn in the skin.

Accordingly, it is desirable to be able to treat the skin by effectivelyheating multiple follicles, without burning the surrounding skin. Such amethod and apparatus should be able to remove more than one hair at atime, and preferably over a wide area of skin, for example at least twosquare centimeters. Additionally, the method and apparatus should becapable of using incoherent light.

SUMMARY OF THE INVENTION

According to a first embodiment of the invention a therapeutic treatmentdevice comprises a housing and an incoherent light source, suitably aflashlamp, operable to provide a pulsed light output for treatment,disposed in the housing. The housing has an opening and is suitable forbeing disposed adjacent a skin treatment area. A reflector is mountedwithin the housing proximate the light source, and at least one opticalfilter is mounted proximate the opening in the housing. An iris ismounted coextensively with the opening. Power to the lamp is provided bya variable pulse width forming circuit. Thus, the treatment deviceprovides controlled density, filtered, pulsed light output through anopening in the housing to a skin area for treatment.

According to a second embodiment of the invention a method of treatmentwith light energy comprises the steps of providing a high power, pulsedlight output from a non-laser, incoherent light source and directing thepulsed light output to a treatment area. The pulse width of the lightoutput is controlled and focussed so that the power density of the lightis controlled. Also, the light is filtered to control the spectrum ofthe light.

According to a third embodiment of the invention a coupler comprises anincoherent light source such as a toroidal flashlamp. A reflector isdisposed around the incoherent light source and at least one opticalfiber or light guide. The fiber has an end disposed within thereflector. This end collects the light from the circular lamp. In asimilar coupling configuration fibers may be provided, along with alinear to circular fiber transfer unit disposed to receive light fromthe light source and provide light to the optical fibers. The reflectorhas an elliptical cross-section in a plane parallel to the axis of thelinear flash tube, and the linear flash tube is located at one focus ofthe ellipse while the linear to circular transfer unit is located at theother focus of the ellipse.

The invention further includes the method of treating the skin to removehair from an an area of tissue by producing electromagnetic energy andapplying the energy to the skin. At least one pulse of incoherentelectromagnetic energy is preferably used. The incoherentelectromagnetic energy is then coupled to an area of the surface of thetissue that includes more than one hair follicle.

Additionally, in one alternative embodiment the energy may, but notnecessarily, be produced by pulsing a flashlamp to generate a pulsehaving an energy fluence on the order of 10 to 100 J/cm². The energy canbe coupled through a window in a housing in which the flashlamp islocated, by reflecting the energy to the tissue through the window andthrough a gel located on a surface of the tissue. The window may bebrought into contact with the gel. In other alternative embodiments theangular divergence of the electromagnetic energy is controlled, and thusthe depth of penetration into the tissue, and the coupling to the hairand to the hair follicles, is also controlled. In another alternativeembodiment each step of the method is repeated, but at least two angulardivergences are used, thus obtaining at least two depths of penetration.

In other alternative embodiments, electromagnetic energy is filtered.Specifically, in one embodiment the electromagnetic energy is filteredaccording to the pigmentation level of the tissue to be treated. Inanother alternative, energy that has a wavelength of less than 550 nmand greater than 1300 nm is filtered. Some or all of such energy can befiltered.

In yet another alternative embodiment, the pulse produced has a width ofless than 200 msec, and/or the delay between pulses is on the order of10 to 100 msec between the pulses. In one embodiment, the surface areaof the energy at the tissue is at least two square centimeters.

In accordance with a second aspect of the invention an apparatus forremoving hair from an area of tissue that includes more than one hairfollicle includes a source of pulsed incoherent electromagnetic energy.The source is located within a housing, and a coupler directs theincoherent electromagnetic energy to the surface of the tissue.

According to an alternative embodiment the source is a flashlamp and apulse generating circuit that generates pulses of energy that have anenergy fluence on the order of 10 to 100 J/cm². The coupler can includea transparent window and the housing a reflective interior, wherein theenergy is reflected to the window. A gel is disposed on the surface ofthe tissue and the window is in contact with the gel, to couple theenergy through the window and gel to the surface of the tissue. Inanother alternative embodiment the energy provided by the coupler has arange of angular divergences.

In another alternative embodiment at least one band pass electromagneticfilter is disposed between the source and the tissue. The filter can beselected such that the wavelength of the energy that passes through thefilter is based on the pigmentation level of the treated tissue.Alternatively, the filters pass energy that has a wavelength of between550 nm and 1300 nm.

In other embodiments, the source provides pulses having a width of lessthan 200 msec, and/or delays between pulses on the order of 10 to 100msec. In another embodiment, the area of the energy at the tissue is atleast two square centimeters.

According to a third aspect of the invention, a method of removing hairfrom an area of tissue that has more than one hair follicle includesproducing at least one pulse of electromagnetic energy. A gel on asurface of the tissue cools the tissue, but the gel is not adjacent thehair follicle. The electromagnetic energy is coupled to the surface ofthe tissue.

In one alternative embodiment, the energy is produced by pulsing aflashlamp, and a pulse having an energy fluence on the order of 10 to100 J/cm² is thereby generated. In another embodiment, the flashlamp islocated in a housing that includes a transparent window and the energyis reflected through the window and directed through the gel to thetissue. In yet another alternative embodiment, the angular divergence ofthe electromagnetic energy is selected to determine the depth ofpenetration into the tissue, and to determine the coupling to the hairand to the hair follicles. Also, each step of the method may be repeatedusing at least two different angular divergences, whereby at least twodepths of penetration are obtained.

In another alternative embodiment, the electromagnetic energy isfiltered. The filtering can be done in accordance with the pigmentationlevel of the treated tissue. Alternatively, filtering may includefiltering some or all of the energy that has a wavelength of less than550 nm and greater than 1300 nm.

In another alternative embodiment pulses produced have a width of lessthan 200 msec. The delay between pulses may be on the order of 10 to 100msec. Also, the area of the energy at the tissue can be large, forexample more than two square centimeters. The energy may be incoherent,such as that produced by a flashlamp for example, or coherent, such asthat produced by a laser, for example.

In accordance with another aspect of the invention, an apparatus forremoving hair from an area of tissue that has more than one hairincludes a source of pulsed electromagnetic energy. A gel is disposed onthe surface of the tissue such that the gel cools the tissue but is notadjacent, and does not cool, the hair follicle. A coupler is disposedbetween the source and the surface to couple the energy to the surface.

In one alternative embodiment, the source is a pulsed flashlamp thatgenerates pulses having an energy fluence on the order of 10 to 100J/cm². In another alternative, the flashlamp is located in a housingthat includes a transparent window and a reflective interior. In yetanother alternative embodiment the shape of the coupler determines theangular divergence of the electromagnetic energy, which determines thedepth of penetration of the energy into the tissue, and determines thecoupling to the hair and to the hair follicles. The apparatus mayinclude a band-pass filter disposed between the source and the surface.In one alternative the band-pass filter passes energy having awavelength of between 550 nm and 1300 nm. The source may be a source ofincoherent energy, or a source of coherent energy, such as a laser, forexample.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference is made to theaccompanying drawings, in which like numerals designate correspondingelements or sections throughout, and in which:

FIG. 1 is a cross-sectional view of an incoherent, pulsed light sourceskin treatment device;

FIG. 2 is a side view of the light source of FIG. 1;

FIG. 3 is a schematic diagram of a pulse forming network with a variablepulse width for use with the skin treatment device of FIGS. 1 and 2;

FIG. 4 is a cross-sectional view of a coupler for coupling light from atoroidal flash tube into an optical fiber with a conical edge;

FIG. 5 is a side view of a toroidal flash tube;

FIG. 6 is a top view of a toroidal flash tube;

FIG. 7 shows the geometry for coupling into a conical section;

FIG. 8 is a cross-sectional view of a coupler for coupling light from atoroidal flash tube into an optical fiber with a flat edge;

FIG. 9 is a front sectional view of a coupler for coupling light from alinear flash tube into a circular fiber bundle;

FIG. 10 is a side sectional view of the coupler of FIG. 9;

FIG. 11 is a front view of a coupler for coupling light from a linearflash tube into an optical fiber;

FIG. 12 is a front view of a coupler for coupling light from a linearflash tube into a doped optical fiber;

FIG. 13 is a schematic configuration of a gel skin interface with atransparent plate;

FIG. 14 shows an angular distribution of photons penetrating withoutusing a gel;

FIG. 15 shows a light guide providing a large angular divergence;

FIG. 16 shows a light guide providing a narrow angular divergence;

FIG. 17 shows a spectra produced with a flashlamp current of 200 amps;and

FIG. 18 shows a spectra produced with a flashlamp current of 200 amps;and

FIG. 19 shows a GTO driver circuit for a flashlamp.

FIG. 20 is a schematic drawing of a cross section of a hair follicle inthe dermis and a gel applied to the epidermis in accordance with thepresent invention;

FIG. 21 is a graph showing the optical properties of the skin;

FIG. 22 is a side view of a hair removal apparatus constructed inaccordance with the present invention;

FIG. 23 is a front view of a hair removal apparatus constructed inaccordance with the present invention;

FIG. 24 is a divergent coupler such as one used in the presentinvention; and

FIG. 25 is a non divergent coupler such as one used in the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENTS

Before explaining at least one embodiment of the invention in detail itis to be understood that the invention is not limited in its applicationto the details of construction and the arrangement of the components setforth in the following description or illustrated in the drawings. Theinvention is capable of other embodiments or of being practiced orcarried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein is for the purpose ofdescription and should not be regarded as limiting.

Referring now to FIGS. 1 and 2, cross-sectional and side views of anincoherent, pulsed light source skin treatment device 10 constructed andoperated in accordance with the principles of the present invention areshown. The device 10 may be seen to include a housing 12, having anopening therein, a handle 13 (FIG. 2 only), a light source 14 having anouter glass tube 15, an elliptical reflector 16, a set of opticalfilters 18, an iris 20 and a detector 22 (FIG. 1 only).

Light source 14, which is mounted in housing 12, may be a typicalincoherent light source such as a gas filled linear flashlamp Model No.L5568 available from ILC. The spectrum of light emitted by gas filledlinear flashlamp 14 depends on current density, type of glass envelopematerial and gas mixture used in the tube. For large current densities(e.g., 3000 A/Cm² or more) the spectrum is similar to a black bodyradiation spectrum. Typically, most of the energy is emitted in the 300to 1000 nm wavelength range.

To treat a skin (or visible) disorder a required light density on theskin must be delivered. This light density can be achieved with thefocusing arrangement shown in FIGS. 1 and 2. FIG. 1 shows across-section view of reflector 16, also mounted in housing 12. As shownin FIG. 1, the cross-section of reflector 16 in a plane is perpendicularto the axis of flashlamp 14 is an ellipse. Linear flashlamp 14 islocated at one focus of the ellipse and reflector 16 is positioned insuch a way that the treatment area of skin 21 is located at the otherfocus. The arrangement shown is similar to focusing arrangements usedwith lasers and efficiently couples light from flashlamp 14 to the skin.This arrangement should not, however, be considered limiting. Ellipticalreflector 16 may be a metallic reflector, typically polished aluminumwhich is an easily machinable reflector and has a very high reflectivityin the visible, and the UV range of the spectrum can be used. Other bareor coated metals can also be used for this purpose.

Optical and neutral density filters 18 are mounted in housing 12 nearthe treatment area and may be moved into the beam or out of the beam tocontrol the spectrum and intensity of the light. Typically, 50 to 100 nmbandwidth filters, as well as low cutoff filters in the visible andultraviolet portions of the spectrum, are used. In some procedures it isdesirable to use most of the spectrum, with only the UV portion beingcut off. In other applications, mainly for deeper penetration, it ispreferable to use narrower bandwidths. The bandwidth filters and thecutoff filters are readily available commercially.

Glass tube 15 is located coaxially with flashlamp 14 and has fluorescentmaterial deposited on it. Glass tube 15 will typically be used fortreatment of coagulation of blood vessels to optimize the energyefficiency of device 10. The fluorescent material can be chosen toabsorb the UV portion of the spectrum of flashlamp 14 and generate lightin the 500 to 650 nm range that is optimized for absorption in theblood. Similar materials are coated on the inner walls of commercialfluorescent lamps. A typical material used to generate “warm” whitelight in fluorescent lamps has a conversion efficiency of 80%, has apeak emission wavelength of 570 nm and has a bandwidth of 70 nm and isuseful for absorption in blood. The few millisecond decay time of thesephosphors is consistent with long pulses that are required for thetreatment of blood vessels.

Other shapes or configurations of flashlamp 14 such as circular,helical, short arc and multiple linear flashlamps may be used. Reflector16 may have other designs such as parabolic or circular reflectors. Thelight source can also be used without a reflector and the requiredenergy and power density may be achieved by locating light source 14 inclose proximity to the treatment area.

Iris 20 is mounted in housing 12 between optical filters 18 and thetreatment area and controls the length and the width of the exposedarea, i.e. by collimating the output of flashlamp 14. The length offlashlamp 14 controls the maximum length that can be exposed. Typicallyan 8 cm long (arc length) tube will be used and only the central 5 cm ofthe tube is exposed. Using the central 5 cm assures a high degree ofuniformity of energy density in the exposed skin area. Thus; in thisembodiment the iris 20 (also called a collimator) will enable exposureof skin areas of a maximum length of 5 cm. The iris 20 may be closed toprovide a minimum exposure length of one millimeter. Similarly, thewidth of the exposed skin area can be controlled in the range of 1 to 5mm for a 5 mm wide flashlamp. Larger exposed areas can be easilyachieved by using longer flash tubes or multiple tubes, and smallerexposure areas are obtainable with an iris that more completelycollimates the beam. The present invention provides a larger exposurearea compared to prior art lasers or point sources and is very effectivein the coagulation of blood vessels since blood flow interruption over alonger section of the vessel is more effective in coagulating it. Thelarger area exposed simultaneously also reduces the required proceduretime.

Detector 22 (FIG. 1) is mounted outside housing 12 and monitors thelight reflected from the skin. Detector 22 combined with optical filters18 and neutral density filters can be used to achieve a quick estimateof the spectral reflection and absorption coefficients of the skin. Thismay be carried out at a low energy density level prior to theapplication of the main treatment pulse. Measurement of the opticalproperties of the skin prior to the application of the main pulse isuseful to determine optimal treatment conditions. As stated above, thewide spectrum of the light emitted from the non-laser type sourceenables investigation of the skin over a wide spectral range and choiceof optimal treatment wavelengths.

In an alternative embodiment, detector 22 or a second detector systemmay be used for real-time temperature measurements of the skin duringits exposure to the pulsed light source. This is useful for skinthermolysis applications with long pulses in which light is absorbed inthe epidermis and dermis. When the external portion of the epidermisreaches too high a temperature, permanent scarring of the skin mayresult. Thus, the temperature of the skin should be measured. This canbe realized using infra-red emission of the heated skin, to prevent overexposure.

A typical real-time detector system would measure the infra red emissionof the skin at two specific wavelengths by using two detectors andfilters. The ratio between the signals of the two detectors can be usedto estimate the instantaneous skin temperature. The operation of thepulsed light source can be stopped if a pre-selected skin temperature isreached. This measurement is relatively easy since the temperaturethreshold for pulsed heating, that may cause skin scarring is on theorder of 50° C. or more, which is easily measurable using infra-redemission.

The depth of heat penetration depends on the light absorption andscattering in the different layers of the skin and the thermalproperties of the skin. Another important parameter is pulse width. Fora pulsed ligh source, the energy of which is absorbed in aninfinitesimally thin layer, the depth of heat penetration (d) by thermalconductivity during the pulse can be written as shown in Equation 1:

d=4[kΔt/Cp] ^(1/2)   (Eq. 1)

where

k=heat conductivity of the material being illuminated;

Δt=the pulse-width of the light pulse;

C=the heat capacity of the material;

p=density of the material.

It is clear from Equation 1 that the depth of heat penetration can becontrolled by the pulse-width of the light source. Thus, a variation ofpulse-width in the range of 10⁻⁵ sec to 10⁻¹ sec will result in avariation in the thermal penetration by a factor of 100.

Accordingly, the flashlamp 14 provides a pulse width of from 10⁻⁵ sec to10⁻¹ sec. For treatment of vascular disorder in which coagulation ofblood vessels in the skin is the objective the pulse length is chosen touniformly heat as much of the entire thickness of the vessel as possibleto achieve efficient coagulation. Typical blood vessels that need to betreated in the skin have thicknesses in the range of 0.5 mm. Thus, theoptimal pulse-width, taking into account the thermal properties ofblood, is on the order of 100 msec. If shorter pulses are used, heatwill still be conducted through the blood to cause coagulation, however,the instantaneous temperature of part of the blood in the vessel andsurrounding tissue will be higher than the temperature required forcoagulation and may cause unwanted damage.

For treatment of external skin disorders in which evaporation of theskin is the objective, a very short pulse-width is used to provide forvery shallow thermal penetration of the skin. For example, a 10⁻⁵ secpulse will penetrate (by thermal conductivity) a depth of the order ofonly 5 microns into the skin. Thus, only a thin layer of skin is heated,and a very high, instantaneous temperature is obtained so that theexternal mark on the skin is evaporated.

FIG. 3 shows a variable pulse-width pulse forming circuit comprised of aplurality of individual pulse forming networks (PFN's) that create thevariation in pulse widths of flashlamp 14. The light pulse full width athalf maximum (FWHM) of a flashlamp driven by a single element PFN withcapacitance C and inductance L is approximately equal to:

Δt=2[LC] ^(1/2)   (Eq. 2)

Flashlamp 14 may be driven by three different PFN's, as shown in FIG. 3.The relay contacts R1′, R2′ and R3′ are used to select among threecapacitors C1, C2 and C3 that are charged by the high voltage powersupply. Relays R1, R2 and R3 are used to select the PFN that will beconnected to flashlamp 14. The high voltage switches S1, S2 and S3 areused to discharge the energy stored in the capacitor of the PFN intoflashlamp 14. In one embodiment L1, L2 and L3 have values of 100 mH, 1mH and 5 mH, respectively, and C1, C2 and C3 have values of 100 mF, 1 mFand 10 mF, respectively.

In addition to the possibility of firing each PFN separately, whichgenerates the basic variability in pulse-width, additional variation canbe achieved by firing PFN's sequentially. If, for example, two PFN'shaving pulse-width Δt1 and Δt2 are fired, so that the second PFN isfired after the first pulse has decayed to half of its amplitude, thenan effective light pulse-width of this operation of the system will begiven by the relation: Δt=Δt1+Δt2.

The charging power supply typical has a voltage range of 500 V to 5 kV.The relays should therefore be high voltage relays that can isolatethese voltages reliably. The switches S are capable of carrying thecurrent of flashlamp 14 and to isolate the reverse high voltagegenerated if the PFNs are sequentially fired. Solid-state switches,vacuum switches or gas switches can be used for this purpose.

A simmer power supply (not shown in FIG. 3) may be used to keep theflashlamp in a low current conducting mode. Other configurations can beused to achieve pulse-width variation, such as the use of a single PFNand a crowbar switch, or use of a switch with closing and openingcapabilities.

Typically, for operation of flashlamp 14 with an electrical pulse-widthof 1 to 10 msec, a linear electrical energy density input of 100 to 300J/cm can be used. An energy density of 30 to 100 J/cm² can be achievedon the skin for a typical flashlamp bore diameter of 5 mm. The use of a500 to 650 nm bandwidth transmits 20% of the incident energy. Thus,energy densities on the skin of 6 to 20 J/cm² are achieved. Theincorporation of the fluorescent material will further extend the outputradiation in the desired range, enabling the same exposure of the skinwith a lower energy input into flashlamp 14.

Pulse laser skin treatment shows that energy densities in the range of0.5 to 10 J/cm² with pulse-widths in the range of 0.5 msec are generallyeffective for treating vascular related skin disorders. This range ofparameters falls in the range of operation of pulsed non-laser typelight sources such as the linear flashlamp. A few steps of neutraldensity glass filters 18 can also be used to control the energy densityon the skin.

For external disorders a typical pulse-width of 5 microsecond is used. A20 J/cm electrical energy density input into a 5 mm bore flashlampresults in an energy density on the skin of 10 J/cm². Cutting off thehard UV portion of the spectrum results in 90% energy transmission, orskin exposure to an energy density of close to 10 J/cm². This energydensity is high enough to evaporate external marks on the skin.

Device 10 can be provided as two units: a lightweight unit held by aphysician using handle 13, with the hand-held unit containing flashlamp14, filters 18 and iris 20 that together control the spectrum and thesize of the exposed area and the detectors that measure the reflectivityand the instantaneous skin temperature. The power supply, the PFN's andthe electrical controls are contained in a separate box (not shown) thatis connected to the hand-held unit via a flexible cable. This enablesease of operation and easy access to the areas of the skin that need tobe treated.

The invention has thus far been described in conjunction with skintreatment. However, using a flashlamp rather than a laser in invasivetreatments provides advantages as well. Procedures such as lithotripsyor removal of blood vessel blockage may be performed with a flashlamp.Such a device may be similar to that shown in FIGS. 1 and 2, and may usethe electronics of FIG. 3 to produce the flash. However, to properlycouple the light to an optical fiber a number of couplers 40, 80 and 90are shown in FIGS. 4 and 8-10, respectively.

Coupler 40 includes an optical source of high intensity incoherent andisotropic pulsed light such as a linear flash tube 42, a light reflector44 which delivers the light energy to an optical fiber 46. The latterhas a generally conical edge in the embodiment of FIG. 4. Optical fiber46 transfers the light from light collection system 44 to the treatmentarea. In general, coupler 40 couples pulsed light from a flash tube intoan optical fiber and has applications in medical, industrial anddomestic areas.

For example, coupler 40 may be used in material processing to rapidlyheat or ablate a portion of a material being processed, or to induce aphoto-chemical process. Alternatively, coupler 40 may be used in aphotography application to provide a flash for picture taking. Usingsuch a coupler would allow the flash bulb to be located inside thecamera, with the light transmitted to outside the camera using anoptical fiber. As one skilled in the art should recognize coupler 40allows the use of incoherent light in many applications that coherent orincoherent light has been used in the past.

To provide for coupling the light to an optical fiber, flash tube 42 hasa toroidal shape, shown in FIGS. 5 and 6, and is disposed insidereflector 44. In addition to the toroidal shape other shapes, such as acontinuous helix, may be used for flash tube 42. However, a helical tubeis more difficult to manufacture than a toroidal tube. Referring now toFIG. 6, flash tube 42 is generally in the shape of a tours, but is not aperfect tours since the electrodes located at the end of the tours haveto be connected to the power source. This does not create a significantdisturbance in the circular shape of flash tube 42, since the connectionto the electrodes can be made quite small.

Reflector 44 collects and concentrates the light, and has across-section of substantially an ellipse, in a plane perpendicular tothe minor axis of the toroidal flash tube 42. The major axis of thisellipse preferably forms a small angle with the major axis of toroidallamp 42. The exact value of the angle between the ellipse axis and themain axis of lamp 42 depends on the Numerical Aperture (NA) of theoptical fiber. The toroidal flash tube is positioned so that its minoraxis coincides with the focus of the ellipse. The other focus of theellipse is at the edge of optical fiber 46. Reflector 44 may be machinedfrom metal with the inner surfaces polished for good reflectivity.Aluminum is a very good reflector with high reflectivity in the visibleand ultraviolet wavelengths, and it may be used for this purpose. Thereflector can be machined in one piece and then cut along a surfaceperpendicular to the main axis of the device. This will enableintegration of the toroidal flash tube into the device.

As shown in FIG. 4, the edge of optical fiber 46 is a cone with a smallopening angle, so that the total area of the fiber exposed to the lightfrom the flash tube is increased. Referring now to FIG. 7 the geometryfor coupling light into a conical tip is shown. It is assumed here thatthe light comes from a region in space with a refractive index of n andthat the conical section of the fiber (as well as the rest of the fibercore) has a refractive index of n1.

Not all the light rays hitting the cone are trapped in it. For lightrays that propagate in a plane that contains the major axis of thesystem, a condition can be derived for the angle of a ray that will betrapped and absorbed in the fiber. This condition is shown in Equation3.

Sin (μ_(criti))=Cos (β)−[n ₁ ² /n ₂ ²−1]^(½) Sin (β)  (Eq. 3)

Light will be trapped in the conical portion of the optical fiber if theincidence angle μ is larger than μ_(criti) calculated from Equation 3.Trapping is possible only if n1>n2. If the medium outside of the fiberis air, n₂=1.

Not all of the light trapped in the conical section of the fiber willalso be trapped in the straight portion of the fiber if a fiber with acore and a cladding is used. If a fiber with a core and no cladding isused (air cladding), then all the rays captured in the conical sectionof the fiber will also be trapped in the straight section of the fiber.

The configuration shown in FIG. 4 can also be used with a fluid fillingthe volume between the reflector and the optical fiber. A veryconvenient fluid for this purpose may be water. Water is also veryeffective in cooling the flashlamp if high repetition rate pulses areused. The presence of a fluid reduces the losses that are associatedwith glass to air transitions, such as the transition between theflashlamp envelope material and air. If a fluid is used in the reflectorvolume, then its refractive index can be chosen such that all the raystrapped in the conical section are also trapped in the fiber, even ifcore/cladding fibers are used.

Another way of configuring the fiber in the reflector is by using afiber with a flat edge. This configuration is shown in FIG. 8 and hastrapping efficiency very close to the trapping efficiency of the conicaledge. Many other shapes of the fiber edge, such as spherical shapes, canalso be used. The configuration of the fiber edge also has an effect onthe distribution of the light on the exit side of the fiber and it canbe chosen in accordance with the specific application of the device.

The device may be used with a variety of optical fibers. Single, or asmall number of millimeter or sub-millimeter diameter fibers, willtypically be used in invasive medical applications. In otherapplications, particularly in industrial and domestic applications, itmay be preferable to use a fiber having a larger diameter, or a largerbundle of fibers, or a light guide.

According to one embodiment flexible or rigid light guides are used tocouple the light to the treatment area. Flexible light guides made froma bundle of quartz or other glass fibers that are fused together by heatat the edge of the bundles. The bundles may be circular, rectangular, orany other useful shape. Rigid light guides may be made from quartz,acrylic, glass, or other materials having a high degree of transparency.The material is generally highly polished on all sides.

A typical cross section of a circular light guide useful for therapeutictreatment is one mm to ten mm in diameter. Alternatively, a rectangularlight guide may be used having typical dimensions of 3 mm by 10 mm to 30mm by 100 mm. In either case the length may be 20 to 300 mm, or asneeded for the specific application.

According to another alternative embodiment a rectangular light guide isused to more efficiently couple the light. The rectangular light guideis chosen to have a shape that matches a rectangular linear flashlampand to match the shape of the vessel being treated.

The light guides described above may be used in another alternativeembodiment to control the spectrum of light delivered to the treatmentarea. Spectral control can be achieved by making the light guide from amaterial that had an absorbing dye dissolved therein. Thus, lighttransmitted by the light guide will have a spectrum in as determined bythe absorbing dye. Alternatively, a flat, discrete filter may be addedto one end (preferably the input end) of the light guide. Both of thesefilters are absorbing filters. The inventors have found that absorbingfilters produced by Schott, having Model Nos. OG515, OG550, OG570, andOG590 have suitable characteristics.

Additionally, interference filters or reflective coatings on the lightguide may be used by applying a proper optical coating to the lightguide. Again, a single discrete interference filter could also be used.Additionally, combinations of the various filters described herein, orother filters, may be used. The use of the filters described here mayrender the use of the filters described earlier with reference to FIG. 1redundant.

An alternative embodiment entails the use of application specific lightguides. In this way the spectra of light for various treatments can beeasily controlled. According to this alternative each type of treatmentwill be performed with a specific light guide.

The optical properties of the light guide will be chosen to optimize theparticular treatment. The wavelengths below are particularly useful forthe respective treatments:

arteries less than 0.1 mm in diameter—520-650 nm

veins less than 0.1 mm in diameter—520-700 nm

vessels between 0.1 and 1.0 mm in diameter—550-1000 nm

larger vessels—600-1000 nm

In each case if the skin is darker (higher pigmentation) longerwavelengths on the lower cut-off portion of the spectrum should be used.

Multiple spectra may be used for optimal penetration. This may beaccomplished by illuminating with a few pulses, each having a differentspectrum. For example, the first pulse can have a spectrum that ishighly absorbed in blood. This pulse will coagulate the blood, therebychanging the optical properties of the blood, making it more absorbingin another wavelength range (preferably longer). A second pulse will bemore efficiently absorbed since the blood absorbs energy of a greaterwavelength range. This principle may be used with lasers or other lightsources as well.

In addition to the features of the light guides discussed above, a lightguide is used, in one alternative embodiment, to control the angulardistribution of the light rays impinging on the skin. Light thatimpinges on the skin at large angles (relative to the perpendicular)will not penetrate very deeply into the tissue. Conversely, light thatimpinges perpendicularly to the skin will have a deeper penetration.Thus, it is desirable to provide a distribution of light rays that has arelatively wide angular divergence when the treatment requires shallowpenetration. Alternatively, a narrow divergence is preferable fortreatment requiring deep penetration is desired. Some treatment mightrequire both shallow and deep penetration.

FIG. 15 shows a light guide 115 having an exit beam with a greaterangular divergence than that of the entrance beam. As shown in FIG. 15,a beam 116 enters light guide 115 at a small angle, relative to the axisof light guide 115. When beam 501 exits light guide 115, the angle,relative to the axis, is much greater. The tapered shape of light guide115 enhances this divergence.

FIG. 16 shows a straight light guide 118 that maintains the angulardistribution of the rays of light that enter into it. A beam 119 isshown entering and exiting light guide 118 with the same angle, relativeto the axis of coupler 601. Alternate use of both light guides 115 and118 can achieve the narrow and deep penetration discussed above.Alternatively, the user can select the type of coupler according to thedepth of penetration needed for the treatment being performed.

FIGS. 9 and 10 show a coupler 90 for coupling a linear flash tube 92through a linear to circular fiber transfer unit 94 to a fiber bundle96. A reflector 98 has an elliptical cross-section, shown in FIG. 10, ina plane parallel to the axis of linear flash tube 92 in this embodiment.Tube 92 is located on one focus of the ellipse while the linear side oflinear to circular bundle converter is located at the other focus of theellipse. This configuration is relatively simple to manufacture andcommercially available linear to circular converters such as 25-004-4available from General Fiber Optics may be used. This configuration isparticularly useful for larger exposure areas of the fiber, or for flashillumination purposes.

The energy and power densities that can be achieved by this inventionare high enough to get the desired effects in surface treatment ormedical applications. For the embodiment shown in FIG. 4 the totalenergy and power densities can be estimated as follows. For a typicaltoroidal lamp with a 4 mm bore diameter and a major diameter of 3.3 cman electrical linear energy density input of 10 J/cm into the lamp canbe used with a 5μ sec pulse width. The light output of the lamp will be5 to 6 J/cm for optimal electrical operating conditions. For thereflector shown in FIG. 4, 50% of the light generated in the lamp willreach the lower focus. Thus, a total energy flux on the focus of 25 to30 J may be obtained. For embodiments shown in FIG. 4 or FIG. 8 thetotal cross-section area of reflector at the focal plane has across-section of 0.8 cm². Energy densities on the order of 30 to 40J/cm² at the entrance to the fiber should be attained with thiscross-section. This corresponds to power densities of 5 to 10 MW/cm²,which are the typical power densities used in medical or materialprocessing applications.

For longer pulses, higher linear electrical energy densities into thelamp can be used. For a 1 msec pulse to the flash tube a linearelectrical energy density of 100 J/cm can be used. The correspondingenergy density at the focal area would be up to 300 J/cm². Such energydensities are very effective in industrial cleaning and processingapplications as well as in medical applications.

Alternative embodiments for coupling the optical fiber to an extendedlight source such as a linear flashlamp are shown in FIGS. 11 and 12. Inthe embodiment of FIG. 11 an optical fiber 101 is wound around a lamp102 and a lamp envelope 103. Some of the light that is produced by thelight source is coupled into the fiber. If the light rays arepropagating in the direction that is trapped by the fiber then thislight will propagate in the fiber and it can be used at a fiber output104. One limitation of this configuration is the fact that most of thelight emitted by lamp 103 travels in a direction perpendicular to thesurface of lamp 103 and cannot be trapped in fiber 101.

The embodiment shown in FIG. 12 overcomes this problem. A doped opticalfiber 105 is wound around lamp 102 and envelope 103, rather than anundoped fiber such as fiber 101 of FIG. 11. The dopant is a fluorescentmaterial which is excited by the radiation emanating from lamp 102 andradiates light inside the fiber. This light is radiatedomnidirectionally and the part of it that is within the critical angleof fiber 105 is trapped and propagates through the fiber and can be usedat fiber output 104. The angle of light that is trapped in the fiber isthe critical angle of the material from which the optical fiber oroptical wave guide is made. For a fiber (or optical wave guide) in airthis angle is given by sin α=1/n.

Typically for glass or other transparent materials n=1.5 and α=41.8°.This corresponds to a trapping efficiency of more than 10% of the lightemitted by fluorescence inside the fiber. If we assume a 50% efficiencyof the fluorescence process we find out that more than 5% of the lightproduced by the lamp is trapped and propagated down the fiber. Forexample, a 4″ lamp with a linear electrical energy input of 300 J/inchand 50% electrical to light conversion efficiency would couple 2.5% ofits electrical energy into the fiber. This corresponds, for the 4″ lampcase to a total light energy of 30 J of light. This embodiment has theadditional advantage of transferring the wavelength emitted by the lampto a wavelength that may be more useful in some of the therapeutic orprocessing applications mentioned before. Thus, fluorescent materialdoped in the fiber can be chosen in accordance with an emissionwavelength determined by the specific application of the device.

One alternative embodiment includes the use of a gel to couple the lightto the skin. This alternative reduces heating of the outer layer of theskin (the epidermis and upper layers of the dermis). The gel ispreferably a high viscosity water based gel and is applied to the skinbefore treatment, although other gels that are not necessarily waterbased may be used. A gel having a relatively high heat capacity andthermal conductivity, such as a water based gel, is preferable to enablecooling of the outer skin (the epidermis in particular). Transparency isalso desirable because during treatment light passes through thetransparent gel and reaches the skin.

Referring now to FIG. 13, a gel 110 is applied to the skin 21 prior tothe treatment. A flat layer of gel on top of the skin is used sinceirregularities in the upper layer of the gel through which the lightpasses may cause scattering of the light and reduce its penetration intothe skin. In order to achieve this flatness a solid, transparent, flatpiece 111 may be applied on top of the skin. The configuration is shownschematically in FIG. 13. The transparent plate can be made out of glassor other transparent materials. Either the flashlamp housing or thelight guides discussed above may be placed in direct contact with thetransparent plate.

The configuration of FIG. 13 has the advantage of reducing thescattering of light (represented by arrows 113) that enters into theskin due to irregularities in the surface of the skin. The skin has anindex of refraction that is larger than that of the air. As a result,any photon that impinges on the air skin interface is deflected if itdoes not hit the skin at an incidence angle of 0°. Since the surface ofthe skin is irregular the angular distribution of the skin increases.This is shown schematically in FIG. 14.

The use of gel addresses this problem since the gel can fill irregularvoids that are created by the skin structure. The transparent plate thatcovers the gel and the gel itself will preferably have an index ofrefraction that is close to that of the skin. This is relatively easysince the index of refraction of the skin is of the order of 1.4 in thevisible and the near infrared. Most glasses and transparent plasticshave indices of refraction that are of the order of 1.5 which is closeenough. The index of refraction of water is of the order of 1.34 in thisrange. Water based gels will have similar indices of refraction. Theindex can be increased by proper additives. The plate and gel thus actas a flat surface for the light to impinge upon. Because the gel andplate have an index of refraction close to that of the skin there isvery little scattering at the gel-plate and gel skin interfaces.

The use of a gel has been experimentally successful in the treatment ofleg veins and other benign vascular lesions of the skin. The treatmentswere carried out with the flashlamp described above. However, inalternative embodiments a different incoherent source, or a coherentsource, may be used.

During operation light is typically applied to the skin in a sequence ofthree pulses with short delays between the pulses. This mode ofoperation is used in order to take advantage of the faster cooling ofthe superficial, thin (less than 0.1 mm thick) epidermis compared to thelarger and deeper vessels (typical of leg veins. The gel in contact withthe skin cools the epidermis during the waiting period between thepulses. This cooling reduces significantly the damage to the epidermis.

In accordance with the invention, light is applied to the treated areain either a long pulse or in a sequence of pulses separated by a delay.The delay and/or pulse length is preferably controlled by the operatorto provide enough heat to accomplish the desired treatment but notenough heat to damage the skin.

This concept was tested with large and deep vessels (of the order of 2mm in diameter and 2 mm deep). A thin layer of commercial water basedultrasound gel (1 to 2 mm thick, “Aqua clear” gel made by Parker USA)was applied on the skin. A 1 mm thin glass window was used to generate aflat layer of the gel. The light from the device passed through the thinglass and the gel and into the skin. Care was taken to assure than noair bubbles exist in the gel. This configuration was tested with photonfluences of 30 to 50 J/cm². Coagulation and clearance of the vessels wasobtained without causing damage to the skin. This is contrary to similartrials in which gel was not used and in which fluences of 20 J/cm: withthe same pulse structure caused burns of the skin.

The epidermis has a thickness of approximately 0.1 mm and a cooling timeof about 5 msec. Thus, to avoid burning delays greater than 5 msec areused.

In another alternative embodiment the spectrum of the light used fortreatment is controlled by controlling the voltage and/or currentapplied to the flashlamp. As is well known in the art, the spectrum oflight produced by a flashlamp is dependent on the voltage and currentprovided to the flashlamp. According to this embodiment the inputvoltage and current is selected to provide a desired treatment spectrum.The appropriate voltage and currents may be determined experimentallyfor each flashlamp used.

For example, a flashlamp current of 200 amps produced the spectra shownin FIG. 17. Similarly, the spectra of FIG. 18 was produced using aflashlamp current of 380 amps. The spectra of FIG. 17 shows asignificant enhancement in the wavelength range of 800-1000 nm. Such aspectra is particularly useful for treatment of large vessels.

The different currents and voltages used to control the output spectramay be obtained using a group or bank of capacitors that are capable ofbeing connected in either series or parallel as part of the power sourcefor the flashlamp. A series connection will provide a relatively highvoltage and high current, thereby producing a spectra having energy in ashorter wavelength, such as 500-600 nm. Such a series connection will bemore appropriate for generating shorter pulses (1 to 10 msec, e.g.)useful for treatment of smaller vessels.

A parallel connection provides a lower current and voltage, and thusproduces an output spectra of a longer wavelength, such as 700-1000 nm.Such a spectra is more appropriate for treatment of larger vessels andis suitable for producing longer pulses (in the range of 10-50 msec,e.g.). The selection of series or parallel connections may be done usinga relay or sets of relays.

In one alternative embodiment the pulse forming network of FIG. 3 isreplaced by a GTO driver circuit 121, such as that shown in FIG. 19. Thedriver circuit of FIG. 19 uses a switch capable of being turned both onand off to control the application of power to the flashlamp. While thisalternative embodiment will be described with respect to a GTO beingused as the switch, other switches capable of being turned both on andoff, such as IGBTs, may also be used.

Referring now to FIG. 19, driver circuit 121 includes a high voltagesource 122, a capacitor bank C5, an inductor L5, a diode D5, a switchGTO1, a diode D6, a diode D7, a resistor R5, a capacitor C6, a GTOtrigger generator TR1, a resistor R7, a capacitor C7 and a flashtubetrigger generator TR2. These components are connected to flashlamp 14and serve to provide the power pulses to flashlamp 14. The duration andtiming of the pulses are provided in accordance with the descriptionherein. Driver 121 operates in the manner described below.

High voltage source 122 is connected across capacitor bank C5, andcharges capacitor bank C5 to a voltage suitable for application toflashlamp 14. Capacitor bank C5 may be a comprised of one or morecapacitors, and may be configured in the manner described above.

Prior to illumination of flashlamp 14 flashtube trigger generator TR2breaks down flashlamp 14 and creates a relatively low impedance channeltherein. After the flashlamp breaks down, capacitor C7 dumps currentinto flashlamp 14, further creating a low impedance channel in flashlamp14. In this manner a pre-discharge is provided that prepares flashlamp14 for the power pulse. Capacitor C7 provides a small amount of current,relative to capacitor bank C5. Alternatively, driver circuit 121 mayoperate in a simmer mode, wherein the pre-discharge is not necessary.

Thereafter, switch GTO1 is turned on via a pulse from GTO triggergenerator TR1, completing the circuit between flashlamp 14 and capacitorbank C5. Thus, capacitor bank C5 discharges through flashlamp 14. Aninductor L5 may be provided to control the rise time of the currentthrough flashlamp 14. Inductor L5 may include an inherent resistivecomponent, not shown.

After a length of time determined by the desired pulse width has passed,GTO trigger generator TR1 provides a pulse to switch GTO1, turning itoff. A control circuit determines the timing of the trigger pulses andprovides them in accordance with the desired pulse widths and delays.

A snubber circuit comprised of diode D6, resistor R5, and a capacitor C6is provided for switch GTO1. Also, didoes D5 and D7 are provided toprotect switch GTO1 from reverse voltages. Resistor R7 is provided inparallel with flashlamp 14 to measure the leakage current of switchGTO1, which can in turn be used to make sure that switch GTO1 isoperating properly.

A possible addition to driver circuit 121 is to provide an SCR or otherswitch in parallel with capacitor bank C5. This allows the discharge orresetting of capacitor bank C5 without turning on switch GTO1. Othermodifications may be made, such as providing the circuit with a serialtrigger, rather than the parallel trigger shown. Another modification isto use the driver circuit with a laser rather than flashlamp 14.

Proper use of pulse widths and delays can aid in avoiding burning theepidermis. The epidermis has a cooling time of about 5 msec, while largevessels have a longer cooling time (a 1 mm vessel has a cooling time ofabout 300 msec). Thus, during a pulse of duration longer than 5 msec theepidermis can cool down but the vessel will not. For example, fortreatment of a large vessel (such as one having a diameter of about 1 mma pulse of 100 msec will allow the skin to cool, but the vessel will notcool.

The same effect may be achieved using trains of pulses. This is usefulwhen it is not practical to provide a single long pulse to theflashlamp. The delays between pulses are selected to allow the skin tocool, but to be too short for the vessel to cool. Thus, larger vesselscan be treated with longer delays because they have greater coolingtimes. Small vessels cool quickly and long delays are not effective.However, they also need less energy and can be treated effectively in asingle pulse. Typical delay times are in the range of 20 msec to 500msec. More specifically, delays of between 100-500 msec are effectivefor vessels larger than 1 mm in diameter.

Delays of between 20-100 msec are effective for vessels between 0.5 and1 mm in diameter. Delays of between 10-50 msec are effective for vesselsbetween 0.1 and 0.5 mm in diameter. A single pulse having a width in therange of 1 msec to 20 msec is effective for vessels less than 0.1 mmdiameter.

Additionally, delays should be selected according to skin pigmentation.Darker skin absorbs more energy and needs more time to cool: thus longerdelays are needed. Lighter skin absorbs less energy and can accommodateshorter delays.

It has been found that multiple pulses avoids “purpora” or the explosionof small vessels in or close to the skin. The use of pulses to avoidburning and provide cooling will be effective for light provided bylasers or other sources as well.

Another alternative embodiment includes the use of a microprocessor orpersonal computer to control the flashlamp. The microprocessor can beused to provide the timing functions and prompt the trigger signalsdescribed above. Additionally, in one embodiment the microprocessorincludes a user interface, such as a screen and keyboard, buttons,mouse, or other input device. The microprocessors have informationstored therein that aids in the selection of treatment parameters.

For example, if the condition being treated is a port wine stains skintype III, the physician inputs that condition into the microprocessor.The microprocessor responds with suggested treatment parameters, such asusing a 570 nm cut-off filter, a double pulse with a delay of 50 msecand a fluence of 55 J/cm². The physician can alter these suggestedparameters, but need not refer back to operating guidelines forsuggested parameters. This alternative may be used with light sourcesother than a flashlamp, such as UV or a pulsed laser.

These output parameters are shown on a display such as a screen orprinter, and include the outputs discussed below. This will aid thephysician in determining the proper treatment and in learning how toeffectively use such devices. In one embodiment the microprocessoroutput on the display shows a simulation of interaction of light withskin and vascular lesions, oxygen concentration and temperaturedistribution in malignant tissue being illuminated for the purpose ofcancer by a flashlamp, or processes occurring in skin resurfacing usinginfrared lasers or other sources.

A program within the microprocessor (or alternatively an analog circuit)models interaction of light with tissue and vessels. Many programs maybe used to carry out the modeling, and in the preferred embodiment thefollowing input parameters are used: light source type (flashlamp orpulsed laser e.g.); number of output curves (1-4 e.g.); skin type;vessel diameter and depth; blood type (oxy or deoxy-hemoglobin); pulseduration; delay between pulses; energy fluence; type of filter; short orlong pulse mode; is a gel being used and its temperature. For a pulsedlaser the wavelength is an input (400-1064 nm e.g.).

The microprocessor and the screen show the following information in oneembodiment: temperature distribution in the tissue and in the vessel atthe end of treatment; graphs of up to four curves to compare differentlight sources or treatment regime. Alternatively, the outputs could beprinted rather than shown on a screen.

One skilled in the art will recognize that many microprocessor routinesmay be used to implement the invention. The routines may model theinteractions in many ways, and one such model for single dimensionallight interaction with a tissue uses the following empirical expressionfor fluence:

F=F(0) exp (−x/d)

where

d=1/μ_(eff) and

μ_(eff)=[3μ_(s)(μ_(s)+μ_(s)(1−g))]^(½)

Where μ_(s) is an absorption coefficient of dermis, μ_(s), is ascattering coefficient of dermis, and g is the anisotropy factor whichis defined as average cosine of scattering angle for one scatteringevent.

F(0) was calculated in accordance with Diffusion of Light in TurbidMaterial, A. Ishimaru, Applied Optics, 1989 Vol. 28 No. 12, pp2210-2215, but an empirical correction depending on wavelength is added:

F(0)=Fo(640/W)^(¼)

where W is a wavelength.

Light relaxation time in the tissue is significantly less than thetemperature relaxation time and light pulse durations used for treatmentof skin lesions, therefore a stationary model for description of lightpenetration into the tissue was used. Ishimaru's hydrodynamic model issuitable for calculating of F(0). Accordingly to this model, the diffuseenergy fluence rate ψ_(d) satisfies the following diffusion equation:

(V ² −K ²)ψ_(a) =−Q

Q=3γ_(s)(γ_(τ) +gγ _(a))F _(o) exp (−τ)

k ²=3γ_(s)γ_(a)

γ_(II)=γ_(s)(1−g)+γ_(a)

γ_(l)=γ_(a)+γ_(s)

τ=∫γ_(l) ds

where Fo is the incident energy beam. Scattering and absorptioncoefficients are functions of wavelength. The total energy fluence rateis given by

ψ_(l)=ψ_(a)+ψ_(c)

ψ_(c) =F _(o) exp (−τ)

This equation was calculated numerically with the corresponding boundaryconditions. The boundary condition for ψ_(d) at the surface illuminatedby the incident intensity is

ψ_(d)+2/3γ_(II)·ψ_(d)+2γ_(s) gF _(a)/γ_(IX)=0

Temperature distribution behavior in the tissue is described by solutionof the 1-D heat conductivity equation in planar geometry for nearepidermis area

ρc·∂T/∂T=λ∂ ² T/∂x ²+γ_(a)ψ_(l)

with initial and boundary conditions

T _(T=0)=36

∂T/∂x _(x=0)=0

Here ρ is the density of tissue, c is the specific heat and λ is theheat conductivity coefficient. The thermal properties of water wereassumed for the thermal properties of tissue.

A heat conductivity equation is calculated in cylindrical geometry fornear vessel area, where the center of the cylinder was chosen as pointwith maximal temperature.

ρc∂T/∂γ=λ∂ ² T/∂x ²+1/r·∂T/∂x+γ _(a)ψ_(l)

As one skilled in the art should recognize other models may be used aswell.

The microprocessor or personal computer can also be used to create andstore patient information in a database. Thus, past treatmentinformation such as condition being treated, treatment parameters,number of treatments, etc. is stored and may be recalled when thepatient is again treated. This aids in providing the proper treatment tothe patient. Additionally, the database may include photographs of thepatient's condition before and after each treatment. Again, this aids inrecord keeping and determining what treatments are most successful forgiven conditions.

In addition to the treatments described above the devices and methodsdescribed herein may be used to treat other conditions. For example,psoriasis and warts have been successfully treated. Similarly, skinrejuvenation (treating wrinkles) should be effective. The inventorfurther contemplates using this invention to treat hemorrhoids, throatlesions, and gynecological problems associated with vascularmalformations. In addition, hair depilation can also be effected.

In the use of hair depilation in accordance with the present invention,hair is removed by exposing the “hairy” area to intense, wide area,pulsed electromagnetic (light) energy. The energy heats the hair andcoagulates the tissue around the hair and follicle without damaging thehealthy skin.

An optically transparent water based gel may be applied to the skinprior to treatment. As used herein gel means a viscous fluid that ispreferably, but not necessarily water based. The gel is used to cool theepidermis which is the primary location of light absorption by tissue,due to the melanin content of the epidermis. The gel is applied so asnot to penetrate into the cavity generated by the hair follicle, andthus does not cool the hair and the hair follicle. As a result theenergy is selectively applied to coagulate the hair without damaging theskin.

It is desirable that a spatially dispersed field of light be used fortreatment of the skin, in accordance with the invention. By spatiallydispersed, it is intended that the field of light be spread over anextended area, as would be apparent from the term to one of ordinaryskill in the art. Accordingly, any apparatus or combination of elementssuitable for producing a dispersed field of light on the skin, asopposed to a narrow beam of light on the skin, can be used.

A polychromatic light source, such as a high intensity pulsed flashlamp,is an example of a source suitable for the purposes described herein.One advantage of a polychromatic source such as a flashlamp is thatenergy having a wavelength in the range of 550 to 630 nm is heavilyabsorbed in blood and can be used to coagulate the vessel that feeds thehair. Additionally, longer wavelengths, in the range of 600 to 1100 nmhave a very good penetration into non-pigmented skin. This wavelengthrange can be used to couple to the melanin of the hair. The higherpigmentation of the hair and the hair follicle can enhance theabsorption of energy by the hair.

Flashlamps also have the advantage of being able to illuminate a largearea, thus minimizing the treatment time. The flashlamp combined with aproper reflector can deliver the required fluences to areas on the orderof a few square centimeters in a single application. However, otherlight sources, such as pulsed lasers can be used as well.

Referring now to FIG. 20, a schematic drawing of a cross section of ahair follicle 200 in a dermis 202 is shown. As may be seen in FIG. 20, agel 203 applied to an epidermis 204. In the present invention, waterbased transparent gel 203 is applied to a large section of the skin thatis covered by hair, such as hair 205. Gel 205 is applied to epidermis204 and creates a thin layer on top of epidermis 204. This layer isclosely coupled to epidermis 204 and acts as a heat sink that coolsepidermis 204 when light (electromagnetic energy) is applied to thearea. As may also be seen in FIG. 20, gel 203 does not penetrate into acavity 206 formed by hair follicle 200 due to its surface tensionproperties and the fact that the hair is naturally covered by a thinlayer of fatty material which makes it hydrophobic. The much higher heatdiffusivity of gel 203 compared to that of air which fills cavity 206enables fast cooling of epidermis 204, represented by arrows 207, whilehair 205 is cooled at a much slower rate.

The cooling time—δt of an object that has typical dimensions d anddiffusivity—α can be written as:

δt=d ²/16α

The epidermis has typical cross dimensions of less than 0.1 mm, which isalso the typical diameter of hair. The diffusivity of water isapproximately α=3×10⁻⁹m²sec⁻¹.

The gel is applied, in the manner shown in FIG. 20, over a wide area.When the gel is so applied the typical cooling time of the hair will beon the order of 200 msec and that of the epidermis will be on the orderof 5 msec. This difference in cooling times is due to the fact that thegel does not penetrate into the hair follicles. It is preferable to usea transparent gel since the gel acts only as a cooling agent and shouldnot be heated by the external illumination.

In accordance with the invention, light is applied to the treated areain either a long pulse or in a sequence of pulses separated by a delay.The delay and/or pulse length is preferably controlled by the operatorto provide enough heat to remove the hair but not enough heat to damagethe skin. For example, the pulse length or delay between the pulsesshould be more than the cooling time of the gel covered epidermis andless than the cooling time of the hair and follicle. Thus, referring tothe above discussion on cooling times, a pulse length of 50 msec if asingle pulse is used or a delay of 50 msec between the pulses if a pulsesequence is used are appropriate values. The spectrum of the lightsource may be selected with reference to the absorption by the skin, bythe hair and by the blood vessels feeding the hair. For example, thehair follicle has typical a depth of 1 to 2 mm. It is preferable,therefore, to use a light wavelength range that can penetrate into thisdepth without very high attenuation.

FIG. 21 is a graph showing the scattering, absorption and effectiveattenuation coefficients in fair skin dermis and the absorptioncoefficient of blood in the 400 to 1000 nm range. Because a wide area isilluminated, rather than a single hair, it is preferable to use awavelength range that penetrates into the skin without being highlyattenuated. The skin attenuation coefficient controls the depth ofpenetration of light into the skin. As may be seen in FIG. 21wavelengths that are longer than 550 nm will be more effective topenetrate deep enough into the skin. Shorter wavelengths are lessdesirable because they will be highly attenuated before reaching thelower parts of the hair follicles.

Wavelengths significantly longer than 1,000 nm are also less effectivedue to high absorption of infrared in water which constitutes more than70% of skin. Wide area photo thermal hair removal of the presentinvention preferably uses light that can penetrate deep into the skin,since light is coupled to the hair and the hair follicles only after itpenetrates through the skin. Most of the spectrum of light atwavelengths longer than 1,300 nm is heavily absorbed in water and willbe less useful because it does not penetrate very deep into the skin.For example, CO₂ laser radiation in the 10,000 nm range penetrates onlya few tens of microns into the skin.

Referring now to FIGS. 22 and 23, one preferred embodiment of hairremover 300 includes a flashlamp 301 located in a housing 302 having ahandle. The flashlamp is shown adjacent gel 203 and hairy skin202/204/205. One flashlamp that the inventors have found effective forhair removal is described in detail in co-pending U.S. patentapplication For Method and Apparatus For Therapeutic ElectromagneticTreatment, Ser. No. 07/964,210, filed Oct. 20, 1992 and issued as U.S.Pat. No. 5,405,368, and incorporated herein by reference. The flashlampdescribed therein provides a suitable fluence and it illuminates a largearea in a single pulse (on the order of 10×50 mm).

Such a flashlamp is driven by a variable pulse width power source. Theflashlamp is contained in housing 302 and the light from the flashlampis directed towards the skin by a reflector 305 that has a highreflectivity.

Also shown in FIGS. 22 and 23 is a filter 307, that is disposed betweenflashlamp 301 and gel 203. The filter, or in an alternative embodiment,multiple filters, are used to control the spectrum generated by thelight source. As used herein filter, or band-pass filter, describes adevice that allows electromagnetic energy (light) of certain wavelengthsor frequencies to pass. The other wavelengths or frequencies are eitherpartially or wholly removed.

The operator can select the filter according to the skin pigmentation ofthe person being treated. For the embodiment using a flashlamp, one cantake advantage of the spectral range typically generated by such a lamp,which is in the range of 200 to 1300 nm for high pressure xenonflashlamps operated at high current densities (on the order of 1,000 to5,000 A/cm²). Since hair removal is mainly done for cosmetic reasons andis mostly important for cases of darker hair, the hair itself willabsorb light in a wide spectral range in the visible and the nearinfrared. The shorter wavelengths generated by the flashlamp may beremoved since they do not penetrate as deeply into the skin (as can beseen from FIG. 21).

In one embodiment a long pass filter that transmits only wavelengthslonger than the cut off wavelength of the filter is used. A cut offwavelength of 600 nm is used in a preferred embodiment when the personbeing treated has fair skin. A cut off wavelength in the range of 700 to800 nm is used in the preferred embodiment to treat people with darkskin. According to the invention, the filters may be, for example,dichroic filters or absorbing filters. The desired spectrum can also beachieved by more than one filter or by band-pass filters.

Light from flashlamp 301 is coupled to the skin through a transparentwindow 308 and a coupler 310 (described below). As shown in FIGS. 22 and23, window 308 is placed on transparent water based gel 203. In use, theoperator holds hair remover 300 by handle 304, and places it on the areaof skin where treatment is desired (and gel 203 has been applied).Transparent window 308 creates a well defined flat surface on gel 203,through which light enters into gel 203 and into the skin.

The operator selects the pulse and energy fluence parameters on acontrol unit (not shown). The power and control unit are preferablyhoused in a separate box and will include power from a capacitor chargedto a high voltage by a DC power supply, wherein the capacitor isdischarged through the flashlamp. Hair remover 300 can be connected tothe power and control unit via a flexible cable that allows easy aimingof the device when aiming it to the treatment area on the patient'sskin. Pulse length control can be achieved by using a few pulse formingnetworks that can generate different pulse widths. Alternatively, anopening 309 may include a solid state opening switch that can stop thedischarge at a time preset by the operator, thus controlling the pulsewidth. These elements of the device are well known and can be easilyconstructed, or replaced by similar elements, as one skilled in the artwill know.

After the parameters have been selected, the operator fires the unit bypressing a switch that can be located in a variety of locations. A totalfluence on the order of 10 to 100 J/cm² will successfully remove thehair. This fluence can be determined from the requirement of reaching ahigh enough temperature of the hair and hair follicle, and consideringthe penetration of light, through the skin and into the hair and hairfollicle, absorption of light in the hair and hair follicle, specificheat capacity of the hair and the hair follicle, and the cooling of thehair during the pulse by heat conductivity to the surrounding skin.

Coupler 310 transmits light from flashlamp 301 to gel 203 and to theskin. The coupler can be comprised of a hollow box with internallyreflecting walls that act as a light guide for the light generated byflashlamp 301, to transmit the light (electromagnetic energy) to theskin. Coupler 310 may alternatively be made from other material, forexample, a solid transparent material such as glass or acrylic in whichlight reflection from the walls is achieved by using total internalreflection on the side walls.

Coupler 310 is used, in one alternative embodiment, to control theangular distribution of the light rays impinging on the skin. Light rayswill hit the hair or the hair follicle predominantly when they aretravelling in a direction perpendicular to the plane of the skin. Adistribution of light rays that has a relatively wide angular divergencewhen treating shallow hair is desirable to direct a large portion of theenergy to the hairs and follicles. Conversely, a narrow divergence ispreferable when deep penetration is desired.

In one embodiment both shallow and deep penetration is obtained by ausing a two stage treatment process. A narrow divergence beam is usedfirst to treat the deeper hair follicles, while a high divergence beamis used to treat the top of the hair follicles.

FIG. 24 shows a coupler 501 having an exit beam with a greater angulardivergence than that of the entrance beam. As shown in FIG. 24, a beam502 enters coupler 501 at a small angle, relative to the axis of coupler501. When beam 502 exits coupler 501 the angle, relative to the axis, ismuch greater. The tapered shape of coupler 501 enhances this divergence.

FIG. 25 shows a straight coupler 601, that maintains the angulardistribution of the rays of light that enter into it. A beam 602 isshown entering and exiting coupler 601 with the same angle, relative tothe axis of coupler 601. Alternate use of both couplers 501 and 601 canachieve the narrow and deep penetration discussed above. Alternatively,the user can select the type of coupler according to the depth of hairbeing treated.

Clinical tests have been performed on hair on the legs of a fewpatients. Hair was removed for at least two months without observing anyhair growing back on the exposed areas during this period. Theexperiments were performed with high fluences, i.e., up to 45 J/cm² ineach exposure. The spectrum used covered the range of 570 to 1100 nm andthe fluence was supplied in a triple pulse with delays of 50 to 100 msecbetween pulses. The pulse sequence enabled hair removal with minimumpain and no damage to the skin. The transparent gel that was used inthese experiments was a water based ultrasound gel, such as thatcommonly available.

Thus, it should be apparent that there has been provided in accordancewith the present invention various inventions that fully satisfy theobjectives and advantages set forth above. Although the inventions havebeen described in conjunction with specific embodiments thereof, it isevident that many alternatives, modifications and variations will beapparent to those skilled in the art. Accordingly, it is intended toembrace all such alternatives, modifications and variations that fallwithin the spirit and broad scope of the appended claims.

What is claimed is:
 1. A method for applying electromagnetic radiationto the skin, the method comprising: generating electromagnetic radiationhaving a plurality of wavelengths ranging over the visible section ofthe electromagnetic spectrum and over at least parts of the ultra-violetand infra-red sections of the electromagnetic spectrum; filtering asubstantial part of said plurality of wavelengths in the ultra-violetsection of the electromagnetic spectrum, thereby producing filteredelectromagnetic radiation ranging over a substantial part of the visibleand at least part of the infra-red sections of said generatedelectromagnetic radiation; and applying said filtered electromagneticradiation to the skin.
 2. A method according to claim 1 comprisingapplying a gel to the skin.